Magnetron



Oct. 13, 1953 B. v. ROLLI N 2,655,616

MAGNETRON Filed Aug. 5, 1947 2 Sheets-Sheet 1 FLO. Fuo. 6

IO ls l3 7 A g f INVENTOR l5 l8 n a Bernard v. Roam,

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ATTORNEYS Patented Oct. 13, 1953 signo'r to English Electric 'V'al've "Company, Limited, a'corpoi'ationi'of Great Britain-and North- -ern--Ir'eland Application August 5,1947, Sefial No.-766;2-55 In GIEfit Britain May 24, 1944 Section 1,Publi'c;Law es'mnu ust s, 1946 Patent expires May'24, 1964 "'6 Claims.

v i r V i .ni 1., Iliis'ihvehtion relates to magnetrons andmore particularly to magnetrons 'fo'r producing large amounts of power on a single frequency. Magnetroh's having a central cavity and aplur'ality of cavity resonators open'inginto the central cavity are known, but I have discovered that such magnetrons normally have several modes of oscillation. That is, they oscillate at more than one frequenc single "frequency are desired, the prior art maghetrons are somewhat ineificient in view of the imv'van't'ed oscillations.

This invention has for its primary object to increase the power output or mognetrons. Other f objects include effecting such modes of oscillaitio'n in "the magnetron that power at the desired fre uency is fed to the output coupling more efficiently than power of unwanted frequencies.

Other objects include suppression of undesired 'oscillatioi'ls, and separation of the frequencies of oscillations. Still other objects or the invention will appear to those skilled in "the art as this description proceeds.

If large quantities of power at a 1,0

A practical example, based on actual ex'pe'ri V nent, is now given to show one Way in'which the invention has been carried into effect. A magnetron which oscillated at a frequency corresponding to a wavelength of 1.25 ems. comprised an anode having twelve similar closed-ended cavity resonators of sector section. These cavity resonators were numbered to 12, and the output circuit was connected to resonator No. [2. On the introduction into resonator No, 'l of a piece of glass 6 mm. long, 4 mm. Wide and 0:4 mm. thick (representing a volumeof about cubic mm. or 12 per cent of the total volume of "the resonator and thereby varying its dielectric content and free volume), the power output am the magnetron was nearly doubled as compared with its output in the absence of the "piece of glass, and a discontinuity in the emitted frequency previously found to occur under operating conditions of 12 k. v. and 5,000 oerst'eds could not now be observed. The anode was of the unstrapped type and is believed to have been operating in the mode with azimuth repetition of the oscillatory wave (n=2, where n-lnioWn as the n number-4s the number of repetitions or the wave around the anode).

Further practical embodiments of the invention will now be described with reference to the accompanying drawings in which:

Figure 1 is a cross-sectional view of the resonators of a closed-ended multi-resonator magnetron embodying the present invention;

2 Figure '2 is a section taken along the lin'e 2 -2 of Figure 1;

Figure 3 is a cross-sectional viewof-the'fisonators or a 'l2-vene open-ended 'ma'gnetronein bodying the invention;

Figure 4 is a section taken alon the line -4-4 of Figure 3; I I A Figure 5 is across-sectional view of the resonat ors-of a multi-resonator magnetron inwhich certain of the resonatorshave been modified in accordance with the present invention; Figure 6 is a section taken along the line 66 (if Figure r .7 o.

Figure 7 is aview similarto that of Figure 5 except in greater detail; and g I Figure 8 is a section taken along the line 8--8 ns A Referring now 'to Figures 1 and '2 these show the twelve resonators of a closed-ended magnetron of normal design comprising a central anode "space I around which are arranged the cavity resonators '2 to 13, adjacent cavities being sepa;

rates by similar vanes Hi all integral with and formingpart of the magnetron block I 5 Qavity resonator 5 is formed with a power outlet slo t 1'6 leading to "a waveguide (not shownl The closed ends of the magnetron aredeisgnated I9, 20. This magnetron is modified in 'accordance with the present invention by the insertion of rods I 7 madeof silica in the alternate cavity res- (motors 2, "4, '6, 8, Hi, l2, so as to make the dielecft'r'i'c contents of adjacent resonetorsdifierent. Operation of the magnetron is thereby favored the mode 1i=6-,'and an increase of output 'ob 'tained of approximately 50% as compared with the same magnetron wherein the rods I! are omitted. The stability of operation of the mag.- netron is, moreover, improved. "Figures 3 and 4 shows a 12-resonator magnet'ro'no f open-ended type in which alternate cavity resonators are provided with metal rods l8 so supported at one or both ends that they are not in electrical contact with the walls of the reso-' nators, and do not involve losses due to currents flowingthroush contacts. The free volumes of adjacent resonators are thus made diiierent. The output slot 16 is formed in resonator H. Figures 5 and 6 illustrate a preferred embodi= ment, alternative to that of Figures 3 and 4, but achieving a'similar result; in this case the nant {frequency of each of resonators '2,- 4,8,!!! and His increased as compared with that of resonators 3, 5, 7, 9, H and I3 the effect being to improve the efiiciency of operation of the magnetron and to stabilize it in the mode n=6. This alteration of frequency is eifected by forming alternate resonators of less depth (as measured radially from the central axis A of the magnetron) than their fellows. The output slot 16 is here formed in resonator II, which, as will be seen is one of those of lower frequency, 1. e., one having the greater radial depth and volume. The shallow resonators 2, 4, 6, etc., may be formed by partially filling with conducting material larger resonators similar to 3, 5, 1, etc., but it is preferred to cut, press or hob the resonators to the precise depths required, from a unitary, integral block 15, as shown.

Suitable dimensions for a resonator system of this form are as follows:

Mm. Diameter of cathode (not shown) 2.0 Diameter of central anode space I 4.5 Length of anode block [5 5.0 Diameter between bases of opposing shallow resonators 7.5 Diameter between bases of opposing deeper resonators 9.5 Thickness of vanes between adjacent resonators 0.6

Figures 7 and 8 show further details of the magnetron of Figures 5 and 6. The indirectly heated cathode element 3| is heated by coil 30, and is located between pole pieces 32 and 33. A small portion of magnet 34 is shown. It will be understood, of course, that this magnet extends to both pole pieces 32 and 33 in the usual manner. The anode is connected to the positive side of a high voltage source through lead 35.

I claim:

'1. A multi-resonator magnetron enode member having a central axially extending opening and a plurality of electro-magnetically coupled cavity resonators disposed about and opening into said central opening, each of said resonators having an axial length substantially equal to that of said central opening, and dielectric means in one of said resonators in excess of any dielectric material in another of said resonators to thereby effect an irregularity between said resonators.

2. A magnetron anode block having a central cylindrical main cavity and a plurality of cavity resonators of equal length in the direction parallel to the axis of the main cavity and disposed about and opening into the main cavity, said anode block comprising a peripheral portion and a plurality of vanes of uniform axial length and thickness extending radially inwardly from said peripheral portion toward said main cavity, the opposite sides of each of said vanes being of different depths in directions perpendicular to the axis of said main cavity and adjacent vanes having sides of the same depth facing one another, the peripheral portion and vanes of said anode block constituting the walls of said cavity resonators and defining two groups of resonators of different sizes, the resonators of each group being of identical size and being alternately disposed with respect to the resonators of the other group, and means for extracting power from one of the cavity resonators of the larger size.

3. A magnetron adapted to oscillete at radio frequencies comprising an anode block having a central cylindrical hole and a plurality of cavity resonators disposed about and opening into the central hole, each of said resonators having an axial length substantially equal to that of said central hole, means for establishing a magnetic field substantially parallel to the axis of the central hole, cathode means in the central hole, means for applying a potential difference between the anode and the cathode means with the latter negative, output means for leading off radio frequency energy from one of said cavities, and means for increasing the power output of the magnetron as compared to the output if all cavity resonators had the same volume comprising means adapted to cooperate with alternate cavity resonators for reducing their effective free volumes to volumes which are less than those of the remaining cavities.

4. In a magnetron of the self-excited oscillator type, means for generating radiant energy oscillations of substantially a single predetermined frequency comprising an anode block, said anode block defining a central cylindrical cavity therein and an even number of cavity resonators greater than two symmetrically disposed about said central cavity and opening into said central cavity, said cavity resonators all having walls of predetermined and fixed dimension and being of identical length in directions parallel to the axis of said central cavity, electron emitting means within said central cavity for directing electrons frcm said emitting means to said anode block, means producing a magnetic field in a direction parallel to the axis of said central cavity, output means coupled to one of said cavity resonators, and means producing a frequencyaifecting irregularity in alternately disposed cavity resonators only, exclusive of the resonator to which said output means is coupled, said irregularity producing means being located in a fixed, predetermined position within each of said alternately disposed resonators.

5. A magnetron as claimed in claim 4 wherein said irregularity producin means comprises a piece of solid dielectric material located in each of said alternately disposed cavity resonators.

6. A magnetron as claimed in claim 4 wherein said irregularity producing means comprises a piece of conductive material located in each of said alternately disposed cavity resonators.

BERNARD VINCENT ROLL-IN.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,044,369 amuel June 16, 1936 2,115,521 Fritz et a1 1 Apr. 25, 1938 2,247,077 Blewett et al. June 24, 1941 2,408,234 Spencer ept. 24, 1946 2,409,638 Hansell Oct. 8, 1946 2,419,172 Smith Apr. 15, 1947 2,422,465 Bondley June 17, 1947 2,423,716 McArthur July 6, 1947 2,445,232 Slater July 13, 1948 2,450,629 Bondley Oct. 5, 1948 2,474,893 Heising a- July 5, 1949 2,477,122 Garner July 26, 1949 2,481,151 Powers Sept. 6, 1949 2,585,084 Brown Feb. 12, 1952 FOREIGN PATENTS Number Country Date 730,246 Germany Jan. 8, 1943 

